The main goal of the proposed research is to examine the role of spike-timing-dependent plasticity in the functional modification of the visual cortex. Recent studies performed in the sponsor's laboratory have provided evidence that cortical space representation of cat V1 neurons can be modified by the relative timing of visual stimuli applied to adjacent retinal areas. I will further examine stimulus-timing-dependent cortical modifications with the following specific aims: Aim 1. To determine whether stimulus-timing-dependent modification of space representation is cortical in origin. I will examine whether the modification effect can undergo interocular transfer, which is believed to be intracortical. Aim 2. To determine the spatial specificity and time course of stimulu-timing-dependent modification of cortical receptive fields. I will use asynchronous local two-point stimuli to induce modification of cortical space representation. By varying the position of the conditioning stimuli, the spatial specificity of the modification effect can be determined. Further experiments will be carried out to determine the time course for induction and the persistence of the effect, with an aim to understand the potential roles of spontaneous or ongoing activity in reversing the stimulus-induced modifications. Aim 3. To examine the acute effect of moving stimuli in the induction of cortical modifications, I will investigate the acute effect of moving stimuli in shaping adult cortical receptive fields and its dependence on the velocity of the stimuli, thus providing further evidence for the involvement of spike-timing-dependent plasticity.